A power-assisting device-equipped bicycle has been widely known which can switch a drive source between a human-power and a power-assisting device, such as an electric motor or an internal-combustion engine.
This type of power-assisting device-equipped bicycle is disclosed, for example, in Japanese Patent Application KOKOKU Publication No. 52-37251. In this Publication, a power switching mechanism of a bicycle equipped with a power-assisting device includes a hollow drive gear shaft which has one end portion fixed to a chain drive gear coupled to a rear wheel gear through a chain and which is rotatably supported in a hanger lug of the bicycle, a crank shaft which is rotatably supported in a center bore of the drive gear shaft and which has both end portions fixed to pedal crank arms, a first one-way clutch which is interposed between the crank shaft and the drive gear shaft, an input gear which is rotatably supported on the drive gear shaft and to which a rotation force is transmitted from an internal combustion engine, and a second one-way clutch which is interposed between the drive gear shaft and the input gear. Human power generated by rider is supplied to the crank shaft through pedals and the pedal crank arms and is transmitted through the first one-way clutch to the drive gear shaft and chain drive gear, and further from the chain drive gear through the chain to the rear wheel gear. A rotation force transmitted from the internal combustion engine to the input gear is transmitted through the second one-way clutch to the drive gear shaft and chain drive gear, and further from the chain drive gear through the chain to the rear wheel gear.
However, the above described power-assisting device-equipped bicycle requires a special hanger lug, which is different from the usual hanger lug of an ordinary bicycle, for mounting the power switching mechanism structured as described above, and it is necessary that bicycle using such power-assisting devices specifically designed. As a result, the price of the conventional power-assisting device-equipped bicycles is high.
In recent years, a power-assisting device-equipped bicycle has been known that usually uses human power as a drive source and, when the rider requires an additional drive force greater than a predetermined force, uses a power-assisting device such as a motor or an internal combustion engine, in addition to the human power.
This type of power-assisting device-equipped bicycle is disclosed in, for example, Japanese Patent Application KOKOKU Publication No. 52-33850. A power switching mechanism of this power-assisting device-equipped bicycle includes a hollow drive shaft which has an input gear receiving a rotation force transmitted from an internal combustion engine and which is rotatably supported in a hanger lug of the bicycle, a crank shaft which is rotatably supported in an inner bore of the drive shaft and which has both end portions fixed to pedal crank arms, and a chain drive gear connected through a chain to a rear wheel gear. Human power generated by a rider is supplied to the crank shaft through pedals and the pedal crank arms and is transmitted through the chain drive gear and the chain to the rear wheel gear. Further, when the human power, that is, a drive power, loaded by a rider to the crank shaft becomes a value greater than a predetermined value, an additional rotation force from the internal combustion engine is loaded through the hollow drive shaft to the chain drive gear, in addition to the human power, and is transmitted, together with the human power, through the chain to the rear wheel gear.
This power-assisting device-equipped bicycle also requires a special hanger lug, which in is different from that of the ordinary bicycle, for mounting the power switching mechanism structured as described above, and it is therefore again necessary to provide a specifically designed bicycle. Such a specific design makes the price of this conventional power-assisting device-equipped bicycle high.
In this bicycle equipped with the power-assisting device, moreover, the chain drive gear has a specifically designed structure, which is different from the usual structure of the conventional bicycle, for loading a rotation force from the internal combustion engine to the crank shaft, in addition to the human power, when the human power, that is, a drive force, loaded to the crank shaft becomes a value greater than a predetermined value. The chain drive gear of such a specific structures further increased the price of this conventional power-assisting device-equipped bicycle.
As a rotation drive force transmission device for transmitting a rotation drive force from the power-assisting device to a front wheel or a rear wheel of the bicycle in the conventional power-assisting device-equipped bicycle, a structure is used whereby an output shaft of the power-assisted device is frictionally in contact with the front wheel or the rear wheel of the bicycle. However, the rotation drive force transmission device using the frictional contact is lower in a transmission efficiency of the rotation drive force.
This invention is derived from the above described circumstances, and an object of this invention is to provide a power-assisting device for a bicycle, which can use a body or almost all of the component parts of a conventional bicycle to make the price of the power assisted bicycle low and which can effectively transmit a rotation drive force from the power-assisting device to the wheel of the bicycle, and a bicycle equipped with the above described power-assisting device.